Electrohydraulic plus fuel detonation explosive forming

ABSTRACT

This apparatus provides improved forming with reduced electrode wear by exploding a mixture above a liquid. The liquid rests against a membrane stretched across the lower part of the chamber. When the mixture explodes pressure is exerted through the membrane to form a workpiece against a die.

United States Patent [191 Erlandson 1 July 3, 1973 [54] ELECTROHYDRAULIC PLUS FUEL 3.252.312 5/1966 Maier 72/56 I 2,935,038 5/1960 7 Chatten.... 72/56 DETONATION EXPLOSIVE FORMING 3,127,923 4/1964 Cadwell 72/56 I Inventor: au so a o k, I 3,162,087 12/1964 Lakes 72/56 [7 1 Assignee= Continental Can p y, In FOREIGN PATENTS OR APPLICATIONS New 148,780 4/1961 U.S.S.R 72/63 [22] Filed: Jan. 4, 1971 Primary Examiner-Richard .1. Herbs! [2]] Appl' l03647 Attorney-Americus Mitchell, Joseph E. Kerwin and William A. Dittmann [52] US. Cl...; 72/56, 72/63 [51] Int. Cl 821d 26/08 57 ABSTRACT [58] Field of Search 72/56, 63; 29/421 E This apparatus provides improved forming with re duced electrode wear by exploding a mixture above a F References Cited liquid. The liquid rests against a membrane stretched UNITED STATES PATENTS across the lower part of the chamber. When the mix- 3,188,844 6/1965 Schwinghamer 72/56 ture explodes pressure is exerted through the mem- 3,222,902 12/1965 Bre chaet al.... 72/56 brane to form a workpiece against a i 3,232,085 2/1966 lnoue 72/56 3,371,404 3/1968 Lemelson 72/56 3 Claims, 11 Drawing Figures GASEOUS GASEOUS FUEL OXIDIZER TANK 23 22 7 2| L 1 ill- PATENTEDJUL3 191s 3.742.746

GASEOUS FUEL INVENTG? HQUL M. ERLANDSON 6 1 W ATT Y.

PATENIEUJUL3 191s 3.742.746

- sum. 2 w 5 FUEL TANK OXIDIZER TANK IN VEN TOR PAUL M. ERLANDSCW ATT'Y.

PATENTEUJUU I973 3.74%746 SHEEI 3 0F 5- 'INVENTOR PAUL M. ERLANDSON v PATENIEUJULS 1915 3. 742.746

mm u or 5 I N VENTUR PAUL M. ERLANDSON ATT'Y.

PAIENIEDJULS ms 3.742.746

' sum 5 or 5 I FILTER I LOX IN VEN TOR PAUL M ERLANDSON ATT 'Y ELECTROIIYDRAULIC PLUS FUEL DETONATION EXPLOSIVE FORMING My invention relates to a method and apparatus to provide forming or shaping against a container or other workpiece of deformable material. More specifically, my apparatus provides improved forming with reduced electrode wear by exploding a gas between electrodes and transmitting the pressure through a liquid.

The prior art shows the electrohydraulic forming of metal sheets. In conventional forming by electrohydraulic forming one finds uneven forming pressures causing creep, irregular thinning and adverse stressing. These problems may be found particularly in the case of alloys which do not readily lend themselves to conventional forming. Many of these alloys when worked by conventional methods tend to crack or fracture because of the rapid movement caused by the sharp pressures applied against the entire surface of the workpiece.

It is an object of this invention to provide electrohydraulic forming and fuel detonation forming readily adapted to automation.

It is another object of this invention to provide a vari-.

able forming rate compared to conventional electrohydraulic arcing. The rate provided by this invention is generally slower but may also be faster than that provided by electrohydraulic arcing.

It is a further object of this invention to provide a softer more even forming pressure than is provided by electrohydraulic pressure wave forming.

It is a further object of this invention to provide a pressure which is a combination of two or three pulses.

It is a final object of this invention to provide a fluid forming system which gives more accurate, less abrupt forming to a workpiece which is being formed against a die.

In brief, my invention discloses an electrohydraulic forming device having an explosion chamber with an opening in its bottom and a diaphragm mounted across the opening. Electrodes mounted in the chamber have ignitable gas between them. This gas is ignited by an are passed between the electrodes, or by either means such as a laser pulse-igniter, and the pressure which is developed is transmitted to the diaphragm through a liquid and then to the workpiece which is formed against a die.

The above and other objects will hereafter appear and the nature of the invention is more clearly underthe wheel.

FIG. 5 shows a T section injector with electrodes mounted under a liquid.

FIG. 6 shows a pair of electrodes partially submerged in a liquid with a gas above the liquid.

FIG. 7 shows a coaxial electrode for injecting gas and having a shaped lower reflector.

FIG. 8 shows an embodiment of FIG. 7 taken along the line 88.

FIG. 9 shows another embodiment of FIG. 7 taken along the line 8-8.

FIG. 10 shows encapsulated gas or explosive material with diesel type ignition.

FIG. 11 shows the use of the piezoelectric pump to inject fuel into the prepressured atmosphere above the liquid.

- The chamber 1 shown in FIG. 1 is shaped to provide a reflective wave if pressure is generated in the top 2 of the chamber. This chamber is located in the block member. The chamber 1 is partially filled with an incompressible liquid 4. This liquid may be water or any other type of hydraulic fluid which will serve the purpose of transmitting pressure.

Above the liquid in the chamber is an air space 5. The volume of the liquid in the chamber 1 is somewhat less than the volume of the chamber. Mounted in the air space 5 above the liquid are a pair of electrodes'6, 7 which extend through the forming head into the gas space. These electrodes are mounted in insulators 8', 9 and extend from the outside of the forming head or block member through the forming head wall of the interior of the chamber. The electrode and electrode cir cuit is shown having a capacitor 10 and switch 11 arrangement. When electric current is passed through the electrodes, an are forms between these electrodes in the gaseous combustible mixture now in the upper part of the chamber. The electrode wear may be minimized in comparison to electrode wear caused by arcing in a high dielectric liquid medium. The insulators surrounding the electrodes must be a durable material able to withstand successive impacts. Such a material is nylon, teflon or the like.

The spacing of the electrodes as to each other and the block member must be such that the shortest electrical path is between the electrode tips rather than between an electrode and thewall of the block member. This is critical only when the wall is connected to one of the electrodes.

The gas mixture 5 lying above the liquid is composed of a mixture of an ignitable gas and an oxidizer. Thus, when the high voltage supply is connected through the switch 11 and through the electrode tips 12 the combustible gaseous mixture in the forming head is ignited. Then a pressure impulse is delivered through the liquid 14 and rubber membrane to press the workpiece against the die 14 in a manner similar to conventional techniques now in use. The gas-oxidizer mixture and I ratio can be selected to give controlled velocity forming. Velocities in the range of those achieved with conventional press forming to the higher rates of electrohy-.

draulic and other high energy devices should be practi-.

cal. In a closed die system, the controlled velocity plosive cycle while preventing loss of pressure during the short period of the high level pressure pulse.

Combustion product exit lines 19, are connected to the upper end of the chamber. These lines are small in size and gradually relieve the internal pressures.

Obviously, the timing of the cycle will vary with the speed that the forming head is to be operated.

Acoustical filter elements 21, 22, 23 may be mounted along the lines leading to the combustion chamber. A low-pass acoustical filter may be mounted along the lines to attenuate the explosive impulse in its passage up the lines. The lines 15, 16 leading from the exterior of the forming head to the gaseous chamber have orifices in the interior of the chamber. These orifices 24, 25 are small, they are selected ofa size to emit a continuous flow of fuel and oxidizer but preclude blow back of combustion products during detonation because a rather small orifice provides a large impedence to an extremely high pressure impulse which is of relatively short duration.

The membrane 13 may be mounted on the bottom of the forming head by any other variety of means such as the clamp ring or other mechanical fixtures.

A pressure relief valve 26 may be included to open near the end of the forming cycle and close near the beginning of the fuel and oxidizer injection period. The pressure provided by the exploded mixture and the injected fuel and ozidizer sweeps debris out of the top of the chamber above the top membrane.

The embodiment shown in FIG. 2 is substantially identical to that shown in FIG. 1 except a top membrane 27 provides for separation of the fuel oxidized from the liquid used for pressure transmission. This arrangement precludes the debris of an explosion from contaminating the liquid. Since the liquid remains unchanged the transmission of the impulse through the liquid is unaffected by contamination.

A different system of feeding the fuel and oxidizer may be used as shown in FIG. 3. In this embodiment the electrodes 28, 29 are formed in a cup shaped manner and an oxidizer line 30 and gaseous fuel line 31 may be used to conduct oxidizer or gaseous fuel through one or the other electrode. It is contemplated that gaseous fuel may be conducted through the one electrode and the gaseous oxidizer may be conducted through the other electrode to form a bubble or a combustible mixture between the upper and lower electrodes. The explosion chamber 1 is filled with liquid and a pressure relief valve 26 is provided to eliminate gas products and debris from the chamber prior to each explosion.

The embodiment shown in FIG. 4 shows a multiplicity of forming chambers 32-38 arranged in circular fashion on a common mount. Each forming chamber is equipped with electrodes and fuel and oxidizer conduits. The wheel-like structure 39 rotates around the axle 40 of the common mount. Actual forming of a workpiece 41 would take place only at one station in this arrangement. The cycling of the machine is through the steps of exhaust, combustible gas introduction, oxygen introduction, possible compression, ignition, and finally beginning again with exhaust of the waste products. Removal of debris takes place during the injection of fuel and oxidizer while the wheel is rotating through the 360 of its full cycle. The arrangement of each of the forming chambers is similar to that shown in FIG. 2. Ignition of the combustible gaseous material is accomplished as in FIG. 1 by a spark causing detonation ofthe explosive mixture at the time that this forming chamber is positioned next to the workpiece.

The interior pressure acts against the membrane which presses against the workpiece to form it against a die. The wheel 39 rotates on a axle 40 and is driven by a motor in a conventional fashion.

The explosive compartments of the wheel are mounted on a sleeve 42. Each compartment has two ports in its wall. Conduits 43-56 lead from each port through the block member and to sleeve 42. The sleeve has ports corresponding to the conduits of the block member which pass through the sleeve. The axle itself has a number of passages 57-68 extending along its length and having exit orifices at the rounded part of the axle. These exit orifices are located so as to cooperate with the ports in the sleeve. The paired ports and conduits are located in different planes, in FIG. 4. That is, one of the pair is behind the other. As the sleeve turns the two pairs of exhaust ports and orifices are brought into coaptation, then the pair of compression ports (optional), then a paired combustion gas and exhaust port and orifice, then another paired combustion gas and exhaust and orifice, then oxidizer is forced through ports into the chamber and lastly the sleeve turns to allow the electrical brushes 69, to contact commutator segments 71, 72 and cause an electric arc to jump across the electrodes and ignite the combustible gas mixture. The next station is exhaust. As the wheel turns the entire cycle is repeated. Since this wheel rotates a full 360 between each explosion, sufficient time elapses to permit the full cycle to occur and the gas oxidizing material to mix thoroughly with the fuel prior to detonation. The advantages in this configuration is that it gives a continuous, high speed operation which provides a sufficient time to achieve a proper explosive mixture for detonation.

The compartment shown as vacant may be used or not. A gas bubble detonation fuel combustion chamber 73 is shown in FIG. 5. An appropriate size bubble 74 is necessary to span the gap between the electrodes 75, 76. The size of the bubble is controlled by the rate and amount of gas produced, the internal pressurization of the chamber, the viscosity of the liquid in the chamber and the interelectrode distance. In this embodiment when the bubble 74 comes between the two electrodes, an arc is discharged between the electrodes and the gaseous ignitable material of the bubble ignites to generate a higher pressure within the chamber. Here again, a workpiece is formed against a die by the membrane 77 located at the bottom of the chamber as shown. I-lere, waste is disposed of similarly as in FIG. 1 or a pressure relief valve may be used. Further, the fluid may be removed and replaced and continual recirculation, filtering and recycling of the fluid can take-place. A T shaped mixer tube 78 is used with oxidizer gas under pressure being passed through one arm 79 of the T, the explosive gas through the other arm 80 and the explosive gas mixture being injected into the chamber through the long leg 81 of the T. A mixing chamber may be provided at the juncture of the long leg and the cross arms of the 'I.

The apparatus illustrated in FIG. 6 is designed to obtain a longer controlled combination of two-impulses. This apparatus may or may not operate with a prepressure of from 200 to"800 lb. per sq. in. in the chamber 82. Whether the chamber is prepressured or not, an electric arc is discharged between the electrodes 83, 84 and the arrangement of FIG. 6 develops a controlled combination of two impulses. These two impulses are:

first, an electrically triggered hydraulic impulse and secondly, this is followed by a longer term pressure pulse caused by the combustion of the fuels andozidizers. In summary, there may be a base pre-pressure of 200 to 800 p.s.i. Then when the arc fires, there will be a very sharp pressure peak followed by a lower but still high and longer term pressure pulse.

An arrangement upon which this may be derived is shown in FIG. 6 wherein gas is fed from below the liquid by tubes and bubbles through the liquid to cause a gaseous material to collect above the liquid. In this specific arrangement the thrust of the pressure wave is downward and the pressure pulse causes little blow back into the tubes.

In the embodiment shown in FIG. 7 the combustible gas and oxidizer is mixed and gas is forced down between the upper part of the outer electrode and inner electrode into the lower reflective shaped area of the formed electrode. This reflector can be designed so as to give a pressure wave adapted to operate against any fashion shown in FIG. 5,

In the embodiment of FIG. 7 the explosive mixture is mixed outside of the block member. The inner electrode 87 is a rod extending down the axis of the outer concentric electrode 88. The premixed gas flows through the space 89 between the inner and outer electrodes. When enough of the mixed gas has collected in the lower reflector 90 the switch 91 is closed and the gas is exploded to give a pressure wave-which is shaped by the lower area 90.

A filter and pump in series may be provided to eliminate debris. This arrangement may be in any other embodiment desired.

The inner electrode 87 may be solid or may be hollow as shown in FIG. 9. If it is hollow, oxidizer is passed throughv one conduit and explosive gas is passed through the other.

In the embodiment shown in FIG. 8 an alternative method of mixing is used. The space between the inner electrode and the outer concentric electrode is divided by insulator partition members 92, 93 into two conduits 94, 95. Explosive gas is passed through one conduit and oxidizer ispassed through'the other conduit. In this embodiment mixing of the gases takes place in the lower reflective shaped area 90.

In the embodiment shown in FIG. 10, an electrohydraulic chamber 96 is set up having a membrane 97 across one end. The net effect of the apparatus shown in FIG. 10 is very similar to FIG. 3. The apparatus of FIG. 3 shows two electrodes having curved surfaces between the electrodes 99, 100. These bubbles may be 6 injected through the electrode as shown in FIG. 3 or may be injected into this area from some'outside source 101, 102. Also, bubbles 98 may be an encapsulated explosive gas between the electrode and a diesel type of ignition may be used. The encapsulated gas is disrupted by the relatively high pressure caused by the electrohydraulic impulse. This electrohydraulic impulse and are is continued until almost a total detonation of the encapsulated materials takes place. The fuel-and oxidizer or explosive material are encapsulated in separate. capsules so that they do not mix until the arc fires and the encapsulated material is pressurized and broken. The capsule debris and oxidized material would either be allowed to accumulate before removal after a certain number of firings or may be removed by continual recirculation.

The embodiment shown in FIG. 10 can also be operated with pump to guide a material into the high pressure area. The fuel and oxidizer are mixed in a preceeding stage and are then conducted to a pump and the pump generates a high pressure and drives the fuel and oxidizer into the chamber area under a considerable pressure such as 800 lb. per sq. in. Pressure such as 800 lb. per sq. in. allows for prepressuring or rough forming of a workpiece, followed by coining under the influence of peak pressure.

A piezoelectric pump 103 (FIG. 11) may be used to inject ignitable gas into the space above the liquid. This embodiment is useful in cases where the gas above the liquid is under high pressure and the fuel must be irijected at high pressure but low volume.

The principal of the embodiments above is that by electrohydraulically denotating an explosive gas mixture which mixture is located above a liquid, a composite pressure due to two sources is developed in the liquid. The first component is a sharp pressure impact due to the formation of an electric arc between the electrodes. The second component is a longer term pres sure caused by the burning of the gaseous mixture.

The advantages of this apparatus are the apparatus produces a sharp, very high pressure impulse followed by a sustained fairly high pressure.

Another advantage is reduced electrode wear because of electrically low level ignition impulse and because of an electrically low level ignition impulse passing through the electrodes.

Another advantage is to retain the benefit of the hy-' draulic or an hydraulic medium between the explosion and the workpiece.

Another advantage is a more versitile forming than the appended claims to cover all forms'which" fall within the scope of the invention.

I claim: 1. A forming-device employing electrohydraulic and explosive techniques to form a workpiece comprising: a block member; a chamber formed into said block member and having an opening 'to the exterior of said block member; a liquid partially filling said cavity and touc'hingsaid membrane at all points on one side;

7 8 gaseous mixture filling the space in said chamber chamber; and

above said liquid; a second conduit for conveying a gaseous oxidizer a pair of spaced electrodes mounted in said block into said chamber.

member and extending at least in part into said gas- 3. A forming device employing electrohydraulic and cons mixture; explosive techniques to form a workpiece as set forth conduit means for conveying an ignitable gas and a in claim 2 in which said low pass acoustical filters comgaseous oxidizer into said chamber; and prise: low pass acoustical filters connected to said conduit a first low pass acoustical filter connected to said first means whereby impulse and pressure waves proconduit whereby impulse and pressure waves proceeding up said conduit means are stopped. 10 ceeding up said conduit are stopped; and 2. A forming device employing electrohydraulic and a second low pass acoustical filter connected to said explosive techniques to form a workpiece as set forth second conduit whereby impulse and pressure in claim 1 in which said conduit means comprise: waves proceeding up said conduit are stopped.

a first conduit for conveying an ignitable gas into said 

1. A forming device employing electrohydraulic and explosive techniques to form a workpiece comprising: a block member; a chamber formed into said block member and having an opening to the exterior of said block member; a liquid partially filling said cavity and touching said membrane at all points on one side; gaseous mixture filling the space in said chamber above said liquid; a pair of spaced electrodes mounted in said block member and extending at least in part into said gaseous mixture; conduit means for conveying an ignitable gas and a gaseous oxidizer into said chamber; and low pass acoustical filters connected to said conduit means whereby impulse and pressure waves proceeding up said conduit means are stopped.
 2. A forming device employing electrohydraulic and explosive techniques to form a workpiece as set forth in claim 1 in which said conduit means comprise: a first conduit for conveying an ignitable gas into said chamber; and a second conduit for conveying a gaseous oxidizer into said chamber.
 3. A forming device employing electrohydraulic and explosive techniques to form a workpiece as set forth in claim 2 in which said low pass acoustical filters comprise: a first low pass acoustical filter connected to said first conduit whereby impulse and pressure waves proceeding up said conduit are stopped; and a second low pass acoustical filter connected to said second conduit whereby impulse and pressure waves proceeding up said conduit are stopped. 